The author of the article has outlined the problem of finding the most optimal model of the state for of government, because the necessary condition for stable development of society and effective functioning of the state is to ensure the balance between national interests and the interests of the population of regions and territorial communities. The preconditions, political history and periods of the formation of decentralized power in most European medieval states, scientific positions of national and foreign legal scholars on the expediency of implementing decentralization have been analyzed. It has been found out that the vast majority of Western European countries abdicate the unitary state model by introducing decentralization. The leading idea of reforming is to move the center of solving local issues to the local and, in particular regional level that is achieved by optimizing relations between different levels of territorial organization of power. National traditions, formation and functioning of public agencie in the past, specific features of administrative and territorial structure of the state, existence of autonomous territories, multiethnic population have a significant influence on the formation of the constitutional system on the basis of decentralization in the EU countries. The positive experience Poland, France, Italy, Latvia, Germany and Denmark has been studied. The author has theoretically substantiated that the principle of decentralization has been successfully implemented in the practice of the European Union countries. It has been indicated that the prerequisite for the successful implementation of decentralization processes to create an effective model of governance within the system of decentralized government of Ukraine is: the establishment of the rule of law principle; recognition and guarantees of local self-government; equal legal protection of all forms of ownership; democratic and effective electoral legislation; independence, efficiency, accessibility and transparency of the judicial system, functioning of administrative justice institutions; perfect budget process and high financial discipline; availability of adequate social standards; developed public sector and stable tendency towards its development.